1. Field of the Invention
The present invention relates to wireless data communication networks and more particularly to such a network that employs mobile wireless terminals and that automatically organizes itself for efficient operation.
2. Description of Related Art
Wireless data communications networks may be constructed where a number of (possibly mobile) stations will automatically organize themselves into a hierarchical network. The hierarchical network may contain one or more clusters of stations, each cluster having one cluster head and zero or more cluster members. The cluster heads may operate at a relatively high power level to provide longer distance network links, also known as backbone links, for the network. The cluster members may operate at a lower power in the same frequency band to communicate with the cluster heads. Such self-organizing, or ad-hoc, networks may adaptively reorganize in the face of movement or destruction of cluster heads.
FIG. 1 illustrates a communications network 100 that employs a group of similar (possibly mobile) stations, some of which operate as cluster heads 110. The cluster heads 110 may be interconnected by one or more backbone links 115. Each cluster head 110 defines a cluster, and the cluster may include zero or more cluster members 120. The cluster members 120 communicate directly with the cluster heads 110 through communication links. The dashed line 130 illustrates one such cluster, containing cluster head 110 and two cluster members 120.
The cluster heads 110 and the cluster members 120 may be similar in construction, for example a single model of radio that may transmit at different signal powers. In the exemplary network 100, each station 110/120 may transmit at either a relatively high power level that is suitable for relatively long network links (e.g., cluster heads 110) or at a relatively low power level that is suitable for relatively long or relatively short network links (e.g., cluster members 120). Likewise, each station 110/120 may operate in at least two basic modes. One of the modes (e.g., for cluster heads 110) may be as a “backbone radio” for providing message transit between a number of cluster members and another cluster head. The other mode (e.g., for cluster members 120) may be as a “cluster radio” for providing relatively local message access to the cluster head 110 or to other cluster members 120. The cluster head stations operate at the relatively high power level to communicate with other cluster head stations, and thereby form network backbone 115.
Each station 110/120 has both transmitting and receiving capabilities (i.e. operates as a transceiver). The network 100 may, for example, be operated as a packet switched digital data network for communicating messages from one station to another once its configuration is established. As is understood by those skilled in the art, procedures exist for routing messages over a network, even when the configuration of the network may occasionally change. Likewise, there are procedures for measuring or rating the connectivity of a network in particular configurations.
Though FIG. 1 illustrates a particular interconnection of the various stations 110/120 shown, it should be understood that other patterns of connections are possible. Further, the pattern of connections can change during operation, both to accommodate the introduction of new stations and to allow for the withdrawal or movement of one of the existing stations. The mode of operation of each station may be controlled by an embedded microprocessor in accordance with known network self-organization and communication algorithms.
Using a similar station for both cluster heads 110 and cluster members 120 may result in the overall system 100 being too expensive. For example, if the majority of the stations become configured as cluster members 120, the added functionality for becoming cluster heads in these stations may increase the per-station cost over, for example, dedicated cluster member stations. Further, if both cluster heads 110 and cluster members 120 utilize the same wireless channel, system throughput may suffer. Also, networks that use a single type of transceiver necessarily are limited in future expandability (i.e., incorporating new or different transceivers within the network). Thus, systems with a single transceiver may not be able to employ a mixture of microwave and VHF radio links in a single network, nor a mixture of acoustic and radio links, nor a mixture of infrared broadcast and laser links, etc.
Accordingly, there exists a need for self-organizing communication networks that avoid the shortfalls of such networks that utilize only one type of transceiver for both cluster heads and cluster members.